AuthorTopic: The ol' I/V and op-amp controversy (Read 10628 times)

I ran across this, somewhere. Won't say where, as it is not somewhere any people with any intelligence are found.

(No, it is not Greaser's Palace. A few steps below that. Maybe several.)

Anyway, it was posted a few years back, so no need to post the trivial details of who, when or why. Just putting it here, just to see who it sucks in!

"Andy_c's analysis is fundamentally flawed in that not only does 8x oversampling not reduce slew requirements to 1/8, but a Sigma Delta modulator like the pcm1794 that he mentions could actually slew full scale more than once per sample received from the 8x FIR filter.

That said, I'm not saying that people's ears are broken and that all opamp I/V automatically sounds horrible. But there is really no way ir can compete, and there's hardly reason to use opamps when alternatives are not that much more expensive. Except I guess in portables."

(I left in the typos! Just to be accurate.)

Anyway, the analysis he was referring to was at Greaser's Palace. You can read it here:

I commented the first time. Got excoriated. Learned my lesson, more or less.

Slightly OT... Oddly enough, I've been working on a somewhat higher speed DAC system of late. 2.5 GHz sampling rate. Anyway, guess what one of the challenges is? Making sure the various bypassing arrays don't have resonant points.

Come to think of it, I was excoriated this time as well by a different set of guys. I tell ya - I don't get no respect.

Why are you kvetching? It has 7 inputs, including I2S. What else can you possibly want? Uses mostly through hole................it has to be good!

Plus, this gem:

Quote

The PerfectWave series is assembled, programmed and tested at our new production facility in Boulder Colorado. Instead of the typical production line process, each PWD is hand built by one person from beginning to end. There is a measure of pride of workmanship that goes into every one of these PerfectWave products and it shows from the moment you open the unit up and plug it in.

Translation: We only have one guy building these, in his garage. At least, that is how that would be translated if any of us had a their own stereo company. No farming it out to fancy assembly houses, who make a big pile of them, all at once. No, just one guy, hunched over the PCB, doing it all by himself.

I was wondering... How hard would it be to build a more-or-less discrete R2R ladder DAC (I really mean the converter itself)? I bet with the right FPGA programming, some very good tolerance resistors, and some really good modern CMOS switches it's probably doable.

Back when I was active in the world of building high-end stuff, probably my most famous "claim to fame" was my feedback-less transimpedance I/V. I 'splained some of it, to a guy who worked at our dealer, in Chicago. About 6 months later, he told me they had a new MSB unit in, and it also had a similar I/V.

He proceeded to tell me he 'splained what I 'splained to him to Mark Brasfield. Aka, MSB Technologies. And apologized for opening his big mouth to a competitor.

And some folks still don't understand why I am stingy with what I know, sometimes.

Jocko

Logged

"Major Danby, sir.""Danby. D-A-N-B-Y.""Take him out and shoot him.""Sir?""I said take him out and shoot him. Can't you hear?"